A DTM network is an example of a time-division multiplexed, circuit-switching communication network in which the distribution of access to the bandwidth resources of the network can be dynamically adjusted.
The topology of a DTM network is based upon uni-directional communication on time-division multiplexed bitstreams propagating on optical fibres, wherein each bitstream preferably is accessed by multiple nodes, e.g. in a bus or ring link structure. The bandwidth of each link is divided into 125 μs frames, which in turn are divided into 64-bit time slots. In a system of this kind, write access to time slot is typically distributed among the nodes connected to said bitstream. A node will thus typically have write access to a number of the slots, i.e. to a specific set of slot positions within each recurring frame, and may thereby use these slots for transmission. It may thus only use a slot for transmission if it has write access to this specific slot position.
The distribution of write access to slots among the nodes may typically be changed when so desired or required. For example, write access to a slot may, if so requested or desired, be transferred from one node, typically having access to a surplus of time slots or serving less prioritised applications, to another node that for some reason is in need of transfer capacity.
In an example of such a system, wherein a feature of write access to slots is accompanied by a feature of slot ownership, a first node that owns a slot may, if so desired or required, temporarily lend the actual write access to that slot to a second node that for some reason requires more capacity. In such a case, the second node borrowing the slot will temporarily have the write access to the slot, but will typically be obliged to, at some point in time, return the write access to the slot to the owner of the slot, i.e. to the first node, for example as soon as the second node stops using.
As an example of such a system, WO9736402 discloses a method in a communication network of the afore-mentioned kind, in which the degree of temporary allocation of slots is evaluated, and in which, responsive to the evaluation of temporary allocation, the number of slots being owned by nodes is modified accordingly. That is, the ownership of a slot is transferred from one node to another based on the degree of borrowing of slots.
A problem in these kind of networks is to ensure that the distribution of access to slots is conflict free, i.e. that at no time no two or more nodes on a link regards themselves as having write access to, and thereby risk writing data into, the same slot position. One way of addressing this problem has been to add acknowledgement features in relation to every change in the write access distribution. As an example thereof, when access to a slot is transferred from one node to another, this transfer must be acknowledged by both nodes, and in some systems even by other nodes as well. This feature of acknowledgement has the advantage of limiting the risk of creating access conflicts, but also provides the negative effects of increasing signalling overhead in the network, increasing the number of states that each node must be aware of, thereby increasing the complexity of the design of the nodes, as well as slowing down operation.